Method and apparatus for countergravity casting molten metal

ABSTRACT

A countergravity casting apparatus (10) includes a mold (12) supported above a furnace (14) containing a supply of molten metal to be cast into the mold (12). An electromagnetic pump (66) is accommodated in a casting chamber (46) of the furnace (14) and pumps the metal against gravity from the furnace (14) into the mold (12). The casting chamber (46) is enclosed by an insulating cover (40) and defines an air space over the metal in the chamber (46). A lance (64) extends through the cover (40) and delivers inert gas into the air space and purges it of outside atmospheric gases that would otherwise contaminate the metal in the chamber (46).

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to a method and apparatus for countergravitycasting molten metal in a mold using an electromagnetic pump.

2. Description Of Related Prior Art

Countergravity casting is often used for producing high quality,thin-walled castings. With all known low pressure systems, a castingmold is supported above a vessel containing a supply of molten metal andsome means are provided for delivering the metal against gravity fromthe vessel into the mold. Low pressure countergravity casting enables aslow, tranquil fill of the mold, assuring that even the very thinsections of the casting will be fully developed.

With some systems, the delivery of metal is effectuated by pressurizingthe entire supply of metal in the vessel with air or other gas.Precisely controlling the flow of metal in such systems, however, isdifficult since any change is countered by the momentum of the entiremetal supply. In other words, the entire supply must react to a changein flow for any portion thereof to react.

Other known low pressure systems utilize an electromagnetic pump ratherthan pressurized air for delivering molten aluminum metal into the mold.With such systems, the pump is typically accommodated within the vesseland is responsive to changes in input voltage for delivering only afraction of the metal supply from the vessel into the mold. Since only asmall portion of the metal supply is under pressure at any given time,metal momentum is significantly less a factor when desiring to makechanges in metal flow. Consequently, rapid and frequent changes can bemade to the metal flow for precisely controlling the fill of the mold.

Of those low pressure casting systems known to utilize electromagneticpumps, the pump is most often accommodated in an open well of thevessel. The open well, however, is a source for a tremendous amount ofheat loss as well as contamination of the metal from exposure to theexternal atmosphere. Aluminum metal both oxidizes and picks up hydrogenwhen exposed which, if cast into the mold, produces defects within thecasting.

To account for the heat loss, these systems are known to heat the metalwell above the desired casting temperature which, in turn, producestemperature differences throughout the melt. The temperature variationis harmful to the pump in that it subjects the pump to thermal cyclingand shortens its life. These pumps are very costly. It also affects theviscosity and corresponding flow characteristics of the metal. This isproblematic in that the characteristic output of the pump changes withchanging metal viscosity. Thus, controlling the rate at which metal ispumped into the becomes more difficult.

Another problem with overheating the metal is that aluminum's affinityfor hydrogen increases with increasing temperature thereby furtheradding to the hydrogen contamination of the metal.

One system is known to provide a cover over the well of the vessel forlessening the heat loss and is disclosed in the U.S. Pat. No. 4,967,827to Campbell, granted Nov. 6, 1990. The cover, however, does not protectthe molten metal from contamination by the external atmosphere as theenvironment in the space between the cover and the molten metal is nottaught as being any different from that of the external atmosphere. Assuch, this system presents all of the problems of contamination as thosewith no cover.

Accordingly, there is a need in the industry for a low pressurecountergravity casting system utilizing an electromagnetic pump whichboth insulates the molten metal from heat loss as well as protecting itagainst contamination from the external atmosphere.

SUMMARY OF THE INVENTION AND ADVANTAGES

An apparatus for a countergravity casting molten metal within a mold,comprises: reservoir means having a casting chamber therein forcontaining a supply of the molten metal; a casting mold supported abovesaid reservoir means; electromagnetic pump means associated with saidcasting chamber of said reservoir means and fluidly coupled to said moldfor pumping the molten metal upwardly against gravity from saidreservoir means into said mold, and characterized by cover means fordefining an enclosed air space over the metal in said casting chamberand inert gas purging means for supplying inert gas to the air space andthereby purging the air space of external atmospheric gasses which wouldotherwise react with and contaminate the molten metal in said castingchamber.

A method of casting molten metal against gravity into a casting mold isalso contemplated and includes the steps of melting metal in a meltingfurnace; introducing the molten metal into a casting furnace; disposingan electromagnetic pump in the casting furnace; covering the castingchamber with an insulating cover and defining an enclosed air space overthe metal in the chamber; supplying the enclosed space with inert gas tothereby provide an inert atmosphere to the space and purge it of anyexternal atmospheric gasses which would otherwise react with andcontaminate the metal in the chamber; and actuating the pump and pumpingthe metal against gravity from the casting chamber into anabove-situated casting mold.

The present invention thus provides a countergravity casting systemwhich advantageously employs an electromagnetic pump for preciselycontrolling the countergravity fill of the mold while at the same timeinsulating the metal from heat loss and providing an inert atmosphere tothe molten metal to protect it against contamination from exposure tothe external atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated asthe same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 is a simplified diagrammatic view of an apparatus according tothe present invention;

FIG. 2 is a fragmentary cross sectional view of the fill tubeillustrating the construction and operation of the pressure sensor; and

FIG. 3 is a diagrammatic view of a representative metal pressure versuscasting cycle time ideal fill schedule for a mold.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

A preferred embodiment of an apparatus constructed in accordance withthe present invention is generally shown at 10 in FIG. 1.

The apparatus 10 comprises a casting mold 12 situated above a reservoir14 containing a supply of molten metal 16, such as molten aluminum,which is to be delivered into the mold 12.

The casting mold 12 comprises an upper mold half (cope) 18 which isjoined to a lower mold half (drag) 20 along parting line 22 and defininga mold cavity 24 therebetween. Extending upwardly from a bottom side 26of the mold 12 is a plurality of inlet feed gates 28 establishing fluidcommunication between the mold cavity 24 and the bottom side 26 of themold. The mold 12 is preferably fabricated of resin-bonded silica sandand according to conventional foundry mold making practice but may beconstructed from other conventional foundry mold materials and accordingto other conventional practice. Metal dies may also be used.

The reservoir 14 is a modified 181 Alcoa filtering and degassingcrucible furnace. Such a crucible furnace 14 comprises a metal outershell 30 lined with an insulating refractory liner 32 and accommodatinga crucible or vessel 34 therein. The side walls of the crucible 34 arespaced from the liner 32, which space 36 accommodates induction heatingcoils 38 connected to a suitable power source (not shown) for heatingmolten metal 16 within the crucible 34 and maintaining its temperatureto within ±5° F. of a predetermined casting temperature and, morepreferably, to within ±3° F. of that temperature. With aluminum-basedmetal, the desired casting temperature is between 1250°-1280° F.

An insulated cover 40 has been added to the furnace 14 and comprises ametal plate lined with an insulating refractory material. The cover 40assists the heating coils 38 in maintaining the metal to within thedesired temperature range.

Extending downwardly from the cover 40 and into the crucible 34 is aweir 42 which partitions the crucible 34 into separate receiving andcasting chambers 44 and 46 respectively. The extended free end of theweir 42 is spaced from the bottom of the crucible 34 and provides afluid passageway or opening between the chambers 44 and 46.

The receiving chamber 44 is coupled to a metal supply furnace 48 with aheated and insulated launder or trough 50. The metal supply furnace 48is a commercially available gas reverb high-efficiency type furnace usedfor melting the metal and heating it to approximately the castingtemperature before delivery to the crucible furnace 14. Molten metalfrom the supply furnace 48 is directed into the top of the receivingchamber 44 where it thereafter travels downwardly through the chamber44, beneath the weir 42 and into the casting chamber 46. The receivingchamber 44 has a filter media 52 disposed therein above the fluidpassage in the weir 42 and through which the molten metal 16 must passbefore entering the casting chamber 46. The filter media 52 ispreferably an alumina flake material supported off the bottom of thecrucible 34 by a bed of ceramic beads 54 and similarly covered withanother layer of ceramic beads 56.

Extending down through the cover 40 and into the filter media 52 is alance 58 connected at its inlet side to an inert gas source 60, such asargon or nitrogen, for bubbling inert gas into the filter media 52. Whenthe molten metal is passed through the filter media 52, any undesirableinclusions such as oxides, are trapped and filtered from the metalbefore it enters the casting chamber 46. Further, when casting moltenaluminum metal, the filter media 52 and inert gas together filter outany hydrogen gas dissolved in the aluminum (which has a natural affinityfor hydrogen) before the aluminum enters the casting chamber 46. Thescavenged hydrogen attaches to the argon bubbles introduced into thefilter media 52 and then rises to the surface of the melt with the argonbubbles to prevent the hydrogen from contaminating the molten metal inthe casting chamber 46. Hydrogen is an undesirable component whencasting aluminum since its affinity for hydrogen decreases with coolingcausing the hydrogen to come out of solution in the form of bubblesduring solidification and thereby produce undesirable porosity defectsin the resultant cast article.

The molten metal 16 is maintained at a substantially constant level inthe casting chamber 46 with there being an enclosed air space 62 betweenthe upper surface of the metal 16 and the cover 40 overlying the chamber46. Extending through the cover 40 and into the air space 62 is anotherlance 64 coupled to the same or different inert gas source 60. The lance64 directs a positive flow of the inert gas (e.g., argon or nitrogen)into the air space 62 and purges the space 62 of any externalatmospheric gases which would otherwise react with and recontaminate themetal in the casting chamber 46 with oxide inclusions and hydrogen. Theinert gas thus provides an inert, nonreactive atmosphere to the filteredand degassed metal to protect it against recontamination from theexternal atmosphere. It is insufficient, however, for applying enoughpressure to the metal in the chamber 46 to cause the metal to bedelivered into the mold 12. There is essentially no differentialpressure between the casting chamber 46 and the mold cavity 24 but forthe positive flow of purging gas into the chamber 46 (less than 1 psi).The cover 40 does not seal the chamber 46 air tight but rather enablescontaminating atmospheric gases to escape from the chamber 46 throughthe cover 40 and enables a positive flow of purging gas to be maintainedwithout excessively pressurizing the chamber 46.

Pump means, and preferably an electromagnetic pump 66, is immersed inthe metal contained in the casting chamber 46 of the crucible furnace 14and is responsive to an input voltage applied thereto for pumping themolten metal 16 against gravity from the furnace 14 into the cavity 24of the mold 12 through the bottom feed gates 28 thereof. The pump 66 hasa refractory housing 68 defining a vertical channel 70 extendinginternally therethrough between a bottom inlet and a top outlet thereof.An electromagnet 72 is supported within the housing 68 and is responsiveto the applied voltage for applying electromagnetic energy to the moltenmetal contained in the vertical channel 70 to force it upwardlyaccording to the right hand motor rule. A ceramic porous filter 74covers the inlet of the pump 66 and further filters any oxide inclusionsfrom the metal before delivery into the mold 12. The electromagneticpump 66 may be of any type, such as model PG-450 commercially availablefrom CMI Novacast, Inc., 190 Kelly Street, Elk Groove Village, Ill.60007.

The bottom inlets 28 of the mold 12 are coupled to the outlet of theelectromagnetic pump 66 by a heated vertical delivery system comprisinga heated refractory feed tube 76 and a heated distribution vessel 78.The distribution vessel 78 is supported above the crucible furnace 14 onsupport surface 84 and has heated refractory walls defining a holdingchamber 82 therein. The holding chamber 82 is of appreciably less volumecapacity than either the crucible furnace 14 or the metal supply furnace48.

The feed tube 76 is connected at its bottom end to the outlet of thepump 66 and from there extends vertically upwardly and is coupled to asingle bottom inlet 86 of the distribution vessel 78 for establishingfluid communication between the distribution vessel 78 and the castingchamber 46.

The mold 12 is supported above the crucible furnace 14 by a top wall 88of the distribution vessel 78. The top wall 88 is fabricated ofrefractory material and formed with a plurality of distribution holes 90therethrough corresponding in number, arrangement and approximate sizeto the plurality of bottom feed gates 28 of the mold 12 and in registrytherewith for establishing fluid communication between the holdingchamber 82 and the mold cavity 24. The particular size, number andarrangement of the feed gates 28 and holes 90 are dependent on theconfiguration of the cavity 24 and selected so as to deliver anddistribute the molten metal directly into the cavity 24 at variouslocations without the need for a gating system. A refractory orificegasket or plate 92 is disposed between the mold 12 and distributionvessel 78 and is formed with similarly registered small openings 94therethrough and seals the mold against leakage.

To cast the molten metal 16 from the crucible furnace 14 into thecasting mold 12, a controlled amount of voltage is applied to the pump66 which in turn pumps the metal upwardly into the mold 12 with apressure relating to the applied voltage. Increased voltage produces acorresponding increase in pressure output of the pump 66.

For each casting mold configuration, there exists an ideal manner inwhich the mold cavity should be filled (i.e., a rate of filling themold). This can be expressed in terms of the head pressure of the pumpedmetal (which corresponds to the height of the metal as it rises in themold) versus casting cycle time. A representative ideal metal pressureversus casting cycle time mold filling schedule is illustrated in FIG. 3and indicated generally by the reference numeral character 96.

In order to conform the actual mold filling rate with that of the idealmold filling schedule 96, the apparatus 10 is provided with feedbackcontrol means 98. The control means 98 is a closed-loop system whichcontinuously measures the actual pressure of the pumped metal during thecasting cycle and controls the output of the pump 66 in order to conformthe actual metal pressure with the ideal metal pressure versus castingcycle time mold filling schedule 96. In other words, the feedbackcontrol means 98 monitors the actual rate at which the mold 12 is filledthrough direct measurements of the actual metal pressure and then makesnecessary changes to the voltage supplied to the pump 66 in order toadjust the output of the pump 66 and maintain the actual fillingconditions according to the ideal mold filling schedule.

The feedback control means 98 comprises sensor means 100 forcontinuously sensing the actual pressure of the pumped metal andgenerating feedback information representative of the actual metalpressure. The sensor means 100 includes a pressure sensor 102 and adifferential pressure transducer 104. The pressure sensor 102 is coupledto the feed tube 76 for directly interacting with the pumped metal andsensing changes in actual pumped metal pressure. To accommodate thesensor 102, the feed tube 76 is specially constructed with a verticalmain body portion 106 establishing a generally vertical guide path forthe pumped molten metal from the pump 66 to the distribution vessel 78and a diverging branched portion 108 projecting outwardly and upwardlyin relation to the main body portion 106 by about 45° and is fluidlycoupled with the main body portion 106 for allowing a portion of thepumped metal to enter the branched portion of the tube 76.

A portion of the pressure sensor 102 extends through and into an opendistal end 110 of the branched portion 108 of the feed tube 76 fordirectly interacting with the molten metal therein. The extended throughportion of the sensor means 100 comprises a heat-resistant titaniummetal sleeve 112, the side walls of which define a chamber 114 withinthe sleeve 112. The extended end 116 of the sleeve 112 is open forestablishing fluid communication between the chamber 114 and the fluidpassageway within the feed tube 76. Since the sleeve 112 is accommodatedwithin the branched portion 108, the extended open end 116 of the sleeve112 is directed downwardly toward the crucible furnace 14 as shown inFIG. 2. The other end of the sleeve 112 is formed with a cap 118 whichis welded or otherwise securely fastened to the branched portion 108 forsealing the distal end 110 of a branch portion 108 against metalleakage.

The pressure sensor 102 further includes a capillary tube 120 havinganother chamber 122 therein. The tube 120 is coupled at one of its endsto the cap 118 of the sleeve 112 with the chambers 114, 122 in fluidcommunication and joined at its other end to the pressure transducer104. In a preferred construction, the volume capacity of the chamber 114of the sleeve 112 is at least twice that of the chamber 122 of thecapillary tube 120. This size relationship prevents the pumped metalfrom entering the capillary tube 120 and causing damage thereto.

As metal is being pumped under pressure, a portion of the pumped metalis caused to enter the open end 116 of the sleeve 112 and pressurize apocket of air or other gaseous fluid captured within the chambers 114and 122 of the sleeve 112 and capillary tube 120, respectively. Theamount the molten metal rises in the sleeve 112 determines the amountthe pocket of air within the pressure sensor 102 is pressurized and isrepresentative of the actual metal pressure. Thus, any change in metalpressure is directly sensed by a corresponding change in the pressure ofthe air pocket.

The pressure transducer 104 is responsive to pressurization of the airpocket and generates feedback information in the form of voltage to adigital process controller (DPC) 124 through line 126. The feedbackinformation is also representative of the actual pressure of the pumpedmetal. The DPC is a commercially available unit (Sixnet#60--IOMUXMD-RTU) which has an analog/digital interface or converterbuilt into the unit for converting the analog feedback information intousable digital form.

The feedback control system 98 also includes a programmable logiccontroller (PLC) 128 coupled to both the DPC 124 and the pump 66. ThePLC 128 is commercially available from Texas Instruments, model number545. The PLC 128 is programmed with the ideal reference metal pressureversus casting cycle time mold filling schedule of FIG. 3 and providesthis as set point input information to the DPC 124 through line 130 inthe form of voltage.

The DPC 124 is equipped with comparator means for comparing the actualoutput of the pump provided by the feedback information with the desiredoutput represented by the set point information and then acts to reducethe difference between the two to zero. The DPC 124 acts by generatingdifference valve information provided to the PLC 128 through line 132 inthe form of voltage representative of difference between the feedbackinformation and the set point values. Any difference reflects adiversion from the ideal mold filling schedule 96.

The PLC 128 responds to the difference value information by generatingcontrol signals to the pump 66 through line 134 at preselected controlintervals for correcting the output of the pump in order to reduce thedifference between actual pump output and ideal pump output to zero. Thecontrol signal information to the pump 66 is in the form of correctivevoltage (i.e., increasing, decreasing, or unchanged input voltage) forincreasing, decreasing or maintaining the actual pumped metal pressureaccording to the ideal schedule 96. The PLC 128 delivers a controlsignal to the pump 66 about once every 5 milliseconds.

When casting an article with the subject apparatus 10, the appropriatemold is first selected and positioned on the distribution vessel 78 withthe feed gates 28 aligned with the distribution holes 90.

The PLC 128 is programmed with the ideal mold filling date scheduleinformation of FIG. 3 which indicates that at the start of each castingcycle, the metal is at a bias level B within the distribution vessel 78,which corresponds to a metal pressure of P₀. Between the casting cycletimes t₀ and t₁, the initial pressure is scheduled to be increased fromP₀ to P₁ in order to raise the metal from the bias level B up to theinlets of the mold 12 where it then dwells for a short period from t₁ tot₂. The metal pressure is then scheduled to increase from P₁ to P₂between the times t₂ to t₃ to completely fill mold cavity 24 with moltenmetal.

This filling schedule produces a slow, tranquil fill of the mold 12 andassures that even very thin sections of the mold cavity 24 are filledand that no turbulence is experienced as the metal rises in the mold 12.As shown in FIG. 3, just before the mold cavity 24 has reached thecompletely full mark, the rate of metal pressure increase (i.e., themold fill rate) drops off slightly. This is to prevent hydraulichammering of the molten metal against the upper cavity wall which mightcause metal penetration into the mold, undesirable flashing at theparting line 22, or mold breakage.

At time t₃, the molten metal contacting the cavity walls will havesolidified thereby forming an impenetrable skin or shell around thecasting. The metal in the feed gate inlets 28, however, remains molten.Once the casting is full and the outer skin developed, the metalpressure is scheduled to rapidly increase from P₂ to P₃ over the timeperiod from t₃ to t₄ in order to force additional molten metal into themold cavity 24 to compensate for any shrinkage during solidification ofthe metal in the mold. The over pressure acts as a riser. This overpressure is scheduled to be maintained until the time t₅ at which themetal in the openings 94 of the orifice plate 92 has solidified, afterwhich time the mold is removed and the metal pressure returned to P₀(i.e., the bias level B) in preparation for the next casting.

At all times during the casting cycle, a portion of the pumped metal ispresent in the chamber 114 of the sleeve 112 and is continuouslypressuring the air pocket confined within the sleeve 112 and capillarytube 120. As mentioned, the pressure exerted upon the air pocket isdirectly related to the pressure of the pumped metal. Increasing themetal pressure thus registers as an increase of pressure of the airpocket. The pressure transducer 104 detects the air pocket pressure andsends feedback information in the form of voltage to the DPC 124. Inthis way, the pressure sensor 102 continuously monitors and measures theactual output of the pump 66.

The DPC 124 converts the feedback information into usable digital formand makes comparisons between the actual output of the pump 66 and thedesired ideal output of the pump 66 provided to the DPC 124 from the PLC128 as set point information. From this, the DPC 124 determines whetherthe actual pump output deviates from the desired pump output and thenacts to correct any deviation by sending the difference valueinformation to the PLC 128 in the form of voltage. The PLC 128 thenmakes necessary adjustments to the input voltage to the pump 66 in orderto correct the actual pump output so that it conforms with the desiredideal pump output. The corrective voltage signals from the PLC are sentto the pump 66 once every 5 milliseconds. The pressure is controlledthroughout the entire casting cycle.

It will be appreciated by those skilled in the art that the ideal moldfilling schedule will depend upon the geometry of the mold, the type ofmetal being cast, the design of the casting equipment, etc. The scheduleshown in FIG. 3 is representative of a schedule for casting a cylinderblock of an internal combustion engine in which P₀ =4 psi, P₁ =4.5 psi,P₂ =5.0 psi, P₃ =6.0 psi, t₀ =0 sec, t₁ =2 sec, t₂ =4 sec, t₃ =14 sec,t₄ =15 sec and t₅ =195 sec.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims whereinreference numerals are merely for convenience and are not to be in anyway limiting, the invention may be practiced otherwise than asspecifically described.

What is claimed:
 1. An apparatus for countergravity casting molten metalwithin a mold, comprising:reservoir means (14) having a receivingchamber (44) and a casting chamber (46) therein separated by a partition(42) for containing a supply of the molten metal; a casting mold (12)supported above said reservoir means (14); electromagnetic pump means(66) disposed in said casting chamber (46) and fluidly coupled to saidmold (12) for pumping the molten metal upwardly against gravity fromsaid reservoir means (14) into said mold (12); cover means (40) forcovering said chambers (44, 46) of said reservoir means (14) anddefining an enclosed air space over the metal in said casting chamber(46); filter means (52) disposed in said receiving chamber (44) forfiltering impurities from the metal introduced into said receivingchamber (44) before the metal enters said casting chamber (46);degassing means (58) associated with said receiving chamber (44) forbubbling inert gas into said filter means (52) and thereby scavenginghydrogen gas from the metal passing through said filter means (52)before entering said casting chamber (46); and inert gas purging means(64) associated with said casting chamber (46) for supplying protectiveinert gas directly to the air space and thereby purging the air space ofexternal atmospheric gases which would otherwise react with andrecontaminate the molten metal present in said casting chamber (46) thatwas previously cleansed in said receiving chamber (44).
 2. An apparatusas set forth in claim 1 further characterized by said inert gas purgingmeans (64) comprising a lance extending through said cover means (40)into said air space, said lance (64) being coupled to an inert gassource (60) for delivering inert gas to said air space.
 3. An apparatusas set forth in claim 1 further characterized by said inert gascomprising argon.
 4. An apparatus as set forth in claim 1 furthercharacterized by said inert gas comprising nitrogen.
 5. An apparatus asset forth in claim 1 further characterized by said molten metalcomprising aluminum.
 6. An apparatus as set forth in claim 1 furthercharacterized by said degassing means (58) comprising a lance (58)extending into said filter means (52) and coupled to a source of saidinert gas.
 7. An apparatus as set forth in claim 1 further characterizedby said partition (42) comprising a weir extending down into saidreservoir means (14) from said cover (40) for separating said castingchamber (46) from said receiving chamber (44), said weir (42)terminating short of the bottom of said reservoir means (14) fordefining a fluid passage between said chambers (44), (46) and below saidfilter means (52) for admitting the filtered and degassed metal fromsaid receiving chamber (44) into said casting chamber (46), said weir(42) protecting the metal in said casting chamber (46) againstcontamination from the untreated metal in said receiving chamber (44).8. An apparatus as set forth in claim 1 further characterized by saidfilter means (52) comprising a media of alumina flake material.
 9. Amethod of countergravity casting molten metal into a mold, comprisingthe steps of:melting metal in a melting furnace (48); introducing themolten metal into a receiving chamber (44) of a casting furnace (14);passing the molten metal through a filter media (52) disposed within thereceiving chamber (44) to remove impurities from the molten metal;bubbling inert gas into the filter media (52) to scavenge hydrogen gasfrom the metal as it passes through the filter media (52); passing thecleansed metal around a partition (32) and into a casting chamber (46)of the furnace (14); disposing an electromagnetic pump (66) into thecasting chamber (46); covering the receiving chamber (44) and castingchamber (46) with an insulating cover (40) and defining an enclosed airspace over the cleansed metal within the casting chamber (46);introducing inert gas into the air space of the casting chamber (46) topurge it of any external atmospheric gases which would otherwise reactwith and recontaminate the cleansed metal in the casting chamber (46);and actuating the pump (66) to pump the cleansed metal from the castingchamber (46) upwardly into an above-situated casting mold (12).
 10. Amethod as set forth in claim 9 wherein the molten metal comprisesaluminum-based metal.
 11. A method according to claim 9, wherein theinert gas comprises argon.
 12. A method according to claim 9 wherein theinert gas comprises nitrogen.
 13. A method according to claim 9including heating the metal in the casting furnace (14) and maintainingits temperature to within plus or minus 3° F. of a desired castingtemperature.